Multiple electrical proportioning system



April'19,'1938. 1.. 1.. CUNNINGHAM ET AL 2,114,704

' MULTIPLE ELECTRICAL PROPORTIONING SYSTEM I 7 Filed-July 25, 1935 2 Sheets-Sheet l I leh zlsL Camiflgfiam CZarerzce Wllasall April 1933- 1.. L. CUNNINGHAM T AL' V 2,114,704

MULTIPLE ELECTRICAL PROPORTIONING SYSTEM Filed July 25, 1935 2 Sheets-Sheet 2 WC 'n-f 01: 3 P 3 w[den SI Cufiflingham CZarerzce 7 1. lkfesselZ Patented Apr. 19, 1938 PATENT I OFF-ICE MULTIPLE ELECTRICAL PBOPOBTIONING SYSTEM LewisL. Cunningham,

Minneapolis, Minn, and

- Clarence W. Nessell, Forest Park, Ill., assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application July 25, 1935, Serial No. 33,070

14 Claims.

The present invention relates to an electrical proportioning or follow-up system of the electrical follow-up type that is so arranged that a plurality of follow-up mechanisms or motor 6 means may be concurrently controlled by a single controller, the arrangement being such that each follow-up mechanism or motor means positively moves to a position corresponding to the position oi. the controller, it being impossible for 10 the follow-up mechanism or motor means to become out-ot-step" for any length of time.

Electrical proportioning or follow-up systems of this general character have been in use for a period or time. In one such type, the motor 16 means is controlled by a pair of normally equally energized electromagnetic coils, or a centertapped coil, which control suitable switching mechanism. The energizations of the electromagnetic coils or o! the two portions of the cen- 20 ter-tapped coil have been controlled by the conjoint operation of a controlling potentiometer and a balancing potentiometer, the former being operated in any desired manner, either automatically or manually, and the latter being operated by the motor means.

It is often desirable to control two or more of such motor means or follow-up mechanisms from a single controller or control potentiometer. In the electrically balanced systems of the type herein above described, it has been impossible to have a single controller directly control two or more such follow-up mechanisms since they could get out-of-step" so that the positions o! the various follow-up m or motor means did not correspond to the podtion of the controller. a

In order to obtain a somewhat similar result,

has been usual practice to have one follow-up mechanism or motor means operate a controlling potentiometer tor a second motor means, as well as operate its own balancing potentiometer. In this manner, a number of follow-up mechanisms could be hooked up in tandem. This system, however, has its objection in that the movements 01 all the motor means is not simultaneous, there being a considerable 'delay between movement of the first and last i! any considerable number of motor means were so hooked up in tandem. I

An object of the present invention, therefore,

is the provision of an electrically balanced or electrically operated follow-up or proportioning system which is so arranged that a number of motor means may be simultaneusly and concurrently controlled from a single controller, the 5 electrical arrangement of'the system being such that the various motor means cannot get "outof-step or at least cannot remain out-of-step for any length of time.

More specifically, an object of the present in- 0 vention is the provision of an electrical follow-up system or proportioning system in which each of a plurality of follow-up mechanisms, each comprising a balanced electromagnetic means, contact means, motor means and balancing react- 5 ance means, is electrically interconnected with suitable impedance means in such manner that its particular electromagnetic means can only be balanced by the action 01 its own associated balancing impedance means, even though a plural- 20 ity of such systems are directly connected to a single controlling variable reactance means.

A further object of the invention is the provision of a multiple proportioning system in which a single potentiometer controller directly controls 25 a plurality of balanced relay means, the energlzations oi the balanced relay means being maintained in balance by the action of associated balancing potentiometers driven by motor means controlled by the relay means, suitable imped- 30 ances being so associated with the individual relay means and balancing potentiometers as to insure that each relay means will only be rebalanced upon movement oi the motor means, which it controls, to the position demanded by 35 the controlling potentiometer.

The system of the present invention is, particularly adapted to temperature control systems, and the like, and will be explained in detail in connection with such a system. 40

Further objects of the invention will be found in the drawings, the claims and the detailed description.

The term impedance as used in the specification and claims is intended to mean any device 45 or apparatus by which the flow of electrical current may be varied, and particularly resistance or inductance.

For a more complete understanding of the invention, reference may be had to the following detailed description and accompanying drawings, in which:

Fig. 1 is a digrammatic showing of the limitations of the type of system heretofore used.

Fig. 2 is a diagrammatic showing, similar to Fig. 1, but disclosing the fundamentals oi the system of the present invention, and

Fig. 3 is a diagrammatic showing of a complete application of the present invention.

Referring first to Fig. 1 of the drawings, there is diagrammatically shown the fundamentals of the manner in which a pair of electrical followup systems of the type now utilized in the art would be connected in parallel to a single controller. The single controller is, shown comprising a resistance I8 and a cooperating control contact II. The balancing mechanism of a first follow-up system is indicated by the first balancing resistance I2 and first balancing contact finger I3. Associated with this balancing resistance I2 is a pair of protective resistances I4 and I5. Similarly, the balancing mechanism of the second electrical follow-up mechanism is indicated by a second balancing resistance I6 and a cooperating balance contact I'I. Associated with the balancing resistance I6 is a pair of protective resistances I8 and I 9. The first electrically balanced follow-up system additionally includes a pair of series connected electromagnetic coils 28 and 2| whereas the second electrically balanced follow-up system includes a pair of series connected electromagnetic coils 22 and 23.

Electrical power is shown as being furnished by a step-down transformer 24, having a high voltage primary 25 and a low-voltage secondary 26. It will be noted that the control resistance I8 and the first balancing resistance I2 are comnected in parallel with each other by wires 21 and 28 and are connected in parallel with the seriesconnected electromagnetic coils 28 and 2|, through protective resistances I4 and I5, by wires 29, 38, 3| and 32. Wires 33 and 34 connect the secondary 26 to the wires 38 and 32 so that the electromagneticcoils 28 and 2|, in series, are connected across the secondary 26 and the control resistance I8, as well as the first balancing resistance I2, are connected across the secondary 26 through the protective resistances I4 and I5.

In "a similar manner, the control resistance I8 is connected in parallel with the second balancing resistance I6 by means of wires 21, 28, 35 and 36. Also, this control resistance I8 and the second balancing resistance I6 are connected in parallel with the series-connected electromagnetic coils 22 and 23, through protective resistances I8 and I3, by wires 31, 38, 39 and 48. Wires 33 and 34, and wires 4| and 42 connect the series-connected electromagnetic coils 22 and 23 across the secondary 26 and also connect the controlresistance I8 and second balancing resistance I6, through the protective resistances I8 and I3, across the source 01 power 26.,

The control contact II, the first balancing contact I8, the second balancing contact II, the' junction of electromagnetic coils 22 and 23, and the Junction of electromagnetic coils 28 and 2| are all interconnected by means of wires 43, 44, 46, 46, 41 and 48.

With the parts in the full line position wherein the control contact I I, the first balancing contact I3 and the second balancing contact H are respectively engaged with the mid-portions of control resistance I8, the first balancing resistance I2 and the second balancing resistance l6, ltwill be evident that all or the electromagnetic coils 28,

2|, 22 and 28 are equally energized. Under these conditions, as is well-known in the art, the motor means which controls the balancing potentiometers in electrical follow-up systems of the type referred to herein would be deenergized and the balancing potentiometers would remain stationary.

Now, if the control contact II were moved to the dotted position wherein it engages the extreme right-hand end of control resistance I8, electromagnetic coil 2| of the first follow-up mechanism would be completely short-circuited except for the inclusion of protective resistance I5. This partial short-circuit is as follows: from the junction of electromagnetic coils 20 and 2 I ,wire 48, wire 41, wire 45, wire 43, control contact II, wire 28, wire 3|, protective resistance I5, and wire 32 to the right hand end of electromagnetic coil 2|. Similarly, the electromagnetic coil 23 of the second follow-up mechanism would be completely short-circuited were it not for the protective resistance I9. This substantial short-circuit is as follows: from the junction of electromagnetic coils 22 and 23, wire 41, wire 45, wire 43, control contact I, wire 28, wire 36, wire 39, protective resistance l9, and wire 40 to the right-hand end of electromagnetic coil 23. The electromagnetic coils 20 and 22 are therefore more highly energized than electromagnetic coils 2| and 23'and the two follow-up systems should be operated so as to move their respective balancing contacts I3 and I! along their balancing resistances I2 and I6 towards their left-hand ends to cause rebalancing of the energizations of the two sets of electromagnetic coils.

However, assume that for some reason the balancing contact I I of the second follow-up mechanism did not operate or remained stationary, and that the balancing contact I3 of the first follow-up mechanism was moved to the dotted position shown wherein it engages the extreme left-hand end of its associated balancing resistance l2. Under these conditions, electromagnetic coil 28 is substantially short-circuited, complete short-circuiting being prevented by reason of the inclusion of protective resistance I 4, This partial short-circuit is as follows: from the junction of electromagnetic coils 28 and 2|, wires 48, 41, wire 45, wire 44, balancing contact I3, wire 23, protective resistance I4, and wire 38 to the left-hand end of electromagnetic coil 28. Likewise, the electromagnetic coil 22 is substantially completely short-circuited, complete short-circuiting being prevented by reason of the inclusion of protective resistance I8. I'his partial short-circuit is as follows: from the junction of electromagnetic coils 22 and 23, wire 41:, wire 45, wire 44, balancing contact I3, wire 36, wire 31, protective resistance I8, and wire 38 to the left hand end of electromagnetic coil 22.

the energizations oi the two sets of electromagnetic coils can be balanced out where two of the present type of electrically balanced follow-up systems are connected in parallel with a single controller, even though only one balancing potentiometer has been operated to the proper position. In fact, upon inspection of the system of Fig. 1, it will be seen that the electromagnetic coils will beequally energized whenever any one ,58 and 59 are equal.

of the contacts ll, l8 and I1 is in one extreme position and any other of these remaining contacts is in the opposite extreme position. Therefore, it will be seen that there is no manner of positively providing that the two or more electrically balanced follow-up systems will remain in proper step or proper relation to the position of the control contact ll.

Turning now to Fig. 2, there is a diagrammatic showing of the fundamentals of the system of the present invention. In the showing of Fig. 2, a single controller is indicated by the control resistance 55 and the cooperating control contact A first balancing mechanism is indicated by the balancing resistance 52 and the associated balancing contact 53. The first balancing follow-up system further includes a pair of seriesconnected electromagnetic coils 54 and 55. A second balancing mechanism is indicated by a resistance 55 and a cooperating balancing contact 51. Associated with the balancing resistance 55 and balancing contact 51 is a pair of series-connected electro-magnetic coils 58 and 59. A source of power is indicated by the step-down transformer 55 which is provided with a high voltage primary GI and low voltage secondary 52. The control resistance 55 and-the two sets of series connected electro-magnetic coils 54 and 55 and 55 and 59 are all connected in parallel with each other and across the secondary 52 by wires 53, 54, 55, 55, 51 and 55. The balancing resistance 52 is connected in parallel with its associated series-connected electromagnetic coils 54 and 55, through protective resistances 59 and 15, by wires 1|, 12, 13 and 14.

Similarly, the balancing resistance 55 is connected in parallel with its associated series-connected electromagnetic coils 55 and 59, through protective resistances 15 and 15, by wires 55, 11, 15, 58, 19 and 55. The junction of electromag netic coils 54 and 55 is connected to the associated balancing contact 53 by a wire 5| and is also connected to the control contact 5|, through a resistance 52, by wires 83 and 54. In a like manner, the junction of electromagnetic coils 58 and 59 is connected to the balancing contact 51 by a wire 55, and is connected to the control contact 5|, through a protective resistance 55, by means of wires 51 and 85.

Again, with the parts in the position shown in Fig. 2, it will be evident that the energize.- tions of the electromagnetic coils 54 and 55 and If the control contact 5| .is moved to the dotted position shown wherein it engages the extreme right hand end of control resistance 55, electromagnetic coil 55 will be substantially completely short-circuited, complete short-circuiting being prevented by the resistance 52. This partial short-circuit is as follows: from the junction of electromagnetic coils 54 and 55, wire 53, resistance 52, wire 54, control contact 5|, wire 51 and wire 58 to the right hand end of electromagnetic coil 55. In a similar manner, electromagnetic coil 59 will be substantially completely short-circuited, complete short-circuiting being prevented by reason of the resistance 55. Thispartial short-circuit is as follows: from the junction of electromagnetic coils 55 and 59, wire 51, resistance 85, wire 85, control contact 5|, and wire 51, to the right-hand end of electromagnetic coil 59.

Now assuming that the balancing contact 53 moves to the dotted position wherein it is engaging the extreme left-hand end of its associated balancing resistance 52 and that the balancing contact 51 remains stationary, electromagnetic coil 54 will be substantially completely short-circuited, complete short-circuiting being prevented by reason of the protective resistance 59. This partial short-circuit is as follows: from the junction of electromagnetic coils 54 and 55, wire 5|, balancing contact 53, wire 12, protective resistance 59, and wire 1| to the left-hand end of electromagnetic coil 54. By properly proportioning the protective resistance 59 and the resistance 52, the electromagnetic coils 54 and 55 will now be equally energized. Because of certain other circuits involved, this equal energization of electromagnetic coils 54 and 55 is not obtained by having the resistances 59 and 52 of equal value.

While the energization of electromagnetic coil 58 is changed upon movement of the control contact 5| to the dotted position and movement of the balancing contact 53 to the dotted position, the energizations of electromagnetic coils 55 and 59 are not made equal. For instance, in trying to trace a shunt circuit for electromagnetic coil 55 through its associated protective resistance 15, it will be seen that this shunt circuit is as follows: from the junction of electromagnetic coils 55 and 59, wire 85, balancing contact 51, the left-hand portion of balancing resistance 55, wire 15, protective resistance 15, wire 11, and wire 55 to the left-hand end of electromagnetic coil 55. It will be seen that this shunt circuit not only includes the protective resistance 15 but also includes half of the balancing resistance 55. Therefore, if the protective resistance 15 and the resistance 85 are properly proportioned equal energizations of electromagnetic coils 58 and 59 can only result provided the balancing contact 51 moves to the extreme left-hand end of balancing resistance 55.

In this manner, by segregating the connections between the control contact 5| and the junctions of the sets of electromagnetic coils 54 and 55 and 55 and 59, through the interposition of resistances such as resistances 52 and 55, it has been found impossible to rebalance the energizations of each of the sets of electromagnetic coils 54 and 55 and 58 and 59 unless their respectively associated balancing contacts 53 and 51 move to positions along their balancing resistances 52 and 55 in conformity with the position which the control contact 5| has assumed upon control resistance 55. In this manner, it is positively assured that the various follow-up mechanisms will keep in proper step with the movements of the control contact 5|.

While it would probably be possible to give a number of very detailed and highly complicated electrical theoretical explanations as to why exact positioning of the balancing contacts 53 and 51 must be had in order to equalize the energizations of the respective sets of electromagnetic coils 54 and 55 and 55 and 59, it is thought that the above comparison of the conditions that may arise in the system of Fig. 1 and are prevented by the system of Fig. 2 will sufiice to show the underlying principle of the present invention.

Referring now to Fig. 3, a complete diagrammatic showing of the control of a pair of electrically balanced follow-up systems by a single controller is disclosed. The single controller is shown as a control potentiometer, generally indicated at I55, which comprises a control resistance NH and a cooperating control contact or movable member N12. The control contact I02 may be positioned manually or automatically in any desired manner and is herein shown as controlled by temperature changes, the control element being indicated at I03 and being illustrated as a bimetallic element.

The first electrically balanced follow-up mechanism includes a 'pair of series-connected solenoid coils I04 and I05 that conjointly control the position of a single plunger or armature I06. The armature I06 controls a double-circuit switching mechanism comprised by a switch arm I01 and a pair of cooperating contacts I08 and I09. The arrangement is such that switch arm I 01 may be disposed between contacts I08 and. I09 and not engaging either of them or may be selectively moved into engagement with either of them. This switch arm I01 is connected to plunger I06 by a nonmagnetic connection IIO.

This switching mechanism I01I08I09 controls a balanced relay that includes a pair of series-connected relay windings III and H2. These relay windings III and H2 cooperate in the control of a single plunger or armature H3. The plunger I I3 controls a double-circuit switching mechcanism comprising a switch arm H4 and a pair of spaced cooperating contacts I I 5 and H6. The arrangement is such that switch arm II4 may be disposed between the contacts II 5 and H6 so that it engages neither of them or it may be selectively moved into engagement with either of them. This switch arm I I4 is connected to the plunger II3 by a non-magnetic connection II1.

The switching mechanism II4II5-II6 selectively controls the energization of a pair of high voltage field windings H8 and H9 which form a part of a reversible electric motor means. Associated-with the respective field windings I I8 and H9 are motor rotors I20 and I2I which are secured to a common rotor shaft I22. While the reversible electric motor means has been herein shown as a pair of induction motors, it will be evident that any other suitable type of reversible electric motor means could be utilized.

The rotor shaft I22 is connected to a main operating shaft I23 through suitable reduction gearing indicated at I24. The main operating shaft I 23 may be utilized to position any desired membar and is herein shown as positioning a valve I25 which has a rack I26 connected to its stem I21. A pinion I28 cooperates with the rack I26 and is secured to the main operating shaft I23. The main operating shaft I23 also controls a balancing potentiometer comprising a balancing resistance I29 and a cooperating balancing contact I30 which is secured to or operated by the main operating shaft I23.

The second electrically balanced follow-up system includes a pair of series-connected solenoid coils I35 and I36 which conjointly control an associated plunger or armature I31. This plunger I31 controls a double-circuit open contact switching mechanism that includes a switch arm I38 and a pair of cooperating contacts I39 and I40. The arrangement is such that the switch arm I38 may be disposed intermediate the two contacts I39 and I40 so as to engage neither of them or may be selectively moved into engagement with either of them. The switch arm I38 is connected to plunger I31 by a non-magnetic connection MI.

The switching mechanism I38I39-I40 con trols a balanced relay that includes relay windings I 42 and I 43 which are connected in series. These series connected relay windings I42 and I43 conjointly control the position of a plunger or armature I44. The plunger I44'controls a double-circuit open contact switching mechanism that includes a switch arm I45 and cooperating contacts I46 and I41. Here again, the arrangement is such that the switch arm I45 may be disposed intermediate contacts I46 and I41 so that it engages neither of them or may be selectively moved into engagement with either of them. The plunger I44 is connected to the switch arm I46 by a non-magnetic connection I40.

The switching mechanism I45-I46--I41 selectively controls the energization of a pair of high voltage field windings I49 and I 50. These field windings I49 and I50 respectively cooperate with motor rotors I5I and I52 which are secured to a common rotor shaft I53. It will be evident that the two field windings and two motor rotors comprise a reversible motor means and it is to be understood that any other suitable type of reversible motor means could be utilized.

The rotor shaft I53 is coupled to a main op erating shaft I54 through reduction gearing indicated generally at I55. This main operating shaft I54 may be utilized to position any desired device and is herein shown as controlling a valve I56. The valve I56 is provided with the usual stem I51 to which a rack I58 is secured. A pinion I59 cooperates with the rack I58 and is secured to the main operating shaft I54. The main operating shaft I54 also controls a balancing potentiometer which comprises a balancing resistance I60 and a cooperating balancing contact I 6| which is secured to or operated by the main operating shaft I54. I

Low voltage electrical power is supplied to the controller I00 and to the two electrically balanced follow-up mechanisms by means of a stepdown transformer I10 that is provided with a high voltage primary HI and a low voltage secondary I12. Wires I13 and I14 are connected to the opposite sides of low voltage secondary I12 and may be utilized to supply energy to similar further electrically balanced follow-up mechanisms as will be apparent from an inspection of the drawings.

The control resistance IOI has its opposite ends connected to wires I13 and I14, respectively, by wires I15 and I16. The series-connected solenoid -coils I04 and I 05 are also connected to the wires I13 and I14 by wires I11 and I18. The balancing resistance I29 has its ends connected to wires I 11 and I18 through protective resistances I19 and I80 by wires I8I, I82, I83 and I84. A wire I85 is connected to the bimetallic element I03 and therefore to the control contact I02. The junction of solenoid coils I04 and I05 is connected to this wire I85, through a resistance I86, by wires I81 and I88. The junction of solenoid coils I04 and I05 is further connected to the balancing contact I30 by wires I89 and I90.

The relay windings I II and I I2, in series, are connected to the wires I14 and I13 by wires I9I, I92, I93 and I94. The junction of relay windings III and II 2 is connected to the switch arm I01, through a resistance I95, and to the junction of solenoid coils I04 and I05, through a resistance I96, by wires I91, I98, I99, 200 and I89. The contact I08 is connected to the junction of wires I9I and I92 by a wire 20I and the contact I09 is connected to the junction of wires I93 and I 94 by a wire 202.

The solenoid coils I35 and I36, the relay windings I42 and I43, and all the other associated parts of the second electrically balanced followup mechanism are inter-connected and con- 1' nected to wires I12, I14 and I22 in a manner similar to that just described in connection with the first electrically balanced follow-up mechanism. In other words, the series-connected solenoid coils I25 and I22 are connected to the wires I12 and I14 bywires 2" and 2H. Thebalancing resistance I22 has its opposite ends connected to wires 2" and 2, through protective 2I2 and M2, by wires 2, 2I2, 2I2 and ill. The iunction ofsolenoid coils I22-and I22 is connected I to wire I22, through a resistance 2, by wires 2I2 and 222. This Junction of solenoid coils I22 and I22 is also connected to the balancing contact IN by wires HI and 222.'

The relay windings I42 and I42, in series. are connected to the wires I14 and I12 by wires 222, 224, 222 and 228. The Junction of relay windings I42 and I42 is connected to switch arm I22, through a resistance 221, and to the junction of solenoid coils I25 and I22, through a resistance 222, by wires 222. 222, 22 i, 222, and 22I. Contact I22 is connected to wires 222 and 224 by a wire 222 and contact I42 is connected to wires 225 and 222 by a wire 224.

Operation of the system of Pia. 3

Referring to Fig. 3 of the drawings, it will be noted that the two sets of series-connected solenoid coils I24 and I22 and I22 and I22 and the control resistance I 2| are all connected across the source of power or secondary I12 and are all in parallel with each other. The balancing resistance I28 is in parallel with the series connected solenoid coils I24 and I22 but the protective resistances I18 and I22 are interposed in this circuit. Similarly, the balancing resistance I22 is connected in parallel with the series-connected solenoid coils I25 and I28 except that the protective resistances 2I2 and 2I2 are included in the circuit. The analogy between these parts and the diagrammatic showing of'l lg. 2 should now be apparent. With the parts in the position shown wherein the control contact I22 is engaging the middle of control "I and the two balancing contacts I22 and "I are engaging the middle of balancing resistance I22 and I82, it will be apparent that solenoid coils I24 and, I25 are equally energized and solenoid coils I25 and I28 are equally energized. The switch arms I21 and I22 are therefore disposed intermediate their cooperating contacts I22 and I29 and I28 and I42. The relay windings III and I I2 are therefore equally energized since they are connected in series across the secondary I12 and the relay coils I42 and I42 are equally energized for the same reason. The switch arms [I4 and I45 are therefore disposed intermediate their cooperating contacts H5, H8 and I48 and I41. As a. result, none of the field windings, H2, H8, I49 or I52 is energized and the two main operating shafts I22 and I54 are stationary. The valves I25 and I58 are in half open position.

Now assume that the temperature to which bimetallic element I22 responds should suddenly rise to a point wherein the control contact I22 is moved instantaneously to the extreme right-hand end of control resistance I2I. Solenoid coil I28 is thereupon substantially short circulted,- complete short circuiting being prevented by the res stance I88. This partial short circuit is as follows: from the junction of solenoid coils I24 and I28, wire I21, resistance I22, wire I22, wire I25, bi-metallic element I22, control contact I22; wire I18, wire I14, and wire I12 to the right-hand end of solenoid coil I25. Plunger I22 therefore moves to the left and brings switch arm I21 into engagement with contact I22. Such engagement of arm I21 with contact I22 places the resistance I22 in parallel with the relay winding III and the full fiow of current through relay winding III and resistance I22, in parallel, traverses the relay winding II2. This circuit is as follows: secondary I12, wire I12, wire I24, wire- I22 and relay winding H2, at which point the circuit splits, part going by way of relay winding III, wire "I, wire I22, and wire I12 to the other side of secondary I12, whereas the other portiongoes by way of wire I21, resistance I22, wire I22, switch arm I21, contact I22, wire 22I, and wire I22 to wire I12 and the same side of secondary I12. Engagement of switch arm I21 with contact I22 also sets up an auxiliary flow of. current through solenoid coil I24 and resistance I28 by a circuit which is as follows: secondary I12, wire I12, wire I11, solenoid coil I24, wire I28, wire 222,

resistance I22, wire I82, wire I88, switch arm I2'I,.

contact I22, wire "I, wire I92, and wire I14 to the other side 02 secondary I12. This auxiliary flow of current through the solenoid coil I24 increases the pull on plunger I28 so that switch -arm I21 is held in firm engagement with contact I22.

Since relay winding 2 is now more highly energized than relay winding III, plunger II2 moves to the right and switch arm II4 engages contact II2 whereupon the field winding H2 is energized. The circuit for field winding II! includes a limit switch diagrammatically indicated at 242 which may be operated in any of the usual manners by the main operating shaft I22 so as to limit the movement of shaft I22 in counterclockwise direction as. viewed from the left. The circuit for the field winding H8 is as .follows: line wire 2, switch arm II4, contact II8, wire 242, limit switch 242, wire 242 and field winding II2 to line wire 244. Energization of field winding II2 causes rotation of motor rotor I2l in counter-clockwise direction, as viewed from the left, whereupon main operating shaft I22 is also rotated in counter-clockwise direction as viewed from the left. Balancing contact I32 therefore moves downwardly along balancing resistance I22 towards its lower end and the rack I22 is moved downwardly to vclose valve I25. movement of balancing contact I22 along balancing resistance I22 will continue until the balancing contact I22 engages the extreme lower end of balancing resistance I 28 and is directly connected to the wire I22. When this occurs, the solenoid coil I24 is substantially short circuited, complete short circuiting being prevented by protective resistance I12. This partial short circuit is as follows: from the junction of solenoid coils I24 and I22, wire I22, wire I22, balancing contact I22, wire I22, protective resistance I19, and wire I8I to the left-hand end of solenoid coil I24. The solenoid coils I24 and I25 are now substantially equally energizedagain and the plunger I28 moves iar enough tothe right to disengage switch arm I21 from I22. Whenthis occurs, the resistance I82 is disconnected from its parallel relationship with relay winding III whereupon relay windings III and H2 are again connected in series across the secondary I12 and plunger H2 returns to its central position.- Switch arm II4, therefore, disengages contact H8 and field winding H8 is deenerglzed. This movement of main operating shaft I22 has completely closed valve I28.

Engagement of control contact I22 with the extreme right-hand end of control resistance I2I This / also substantially short-circuits the solenoid coil I36, complete short circuiting being prevented by reason of the inclusion of resistance 2I8. This partial short circuit is as follows: from the junction of. solenoid coils I35 and I33, wire 2| 9, resistance 2I8, wire 228, wire I85, bi-metallic element I83, control contact I82, wire I13, wire I14, and wire 2 to the right-hand end of solenoid coil I33. Plunger I31 thereupon moves to the left and switch arm I38 moves into engagement with contact I39. Engagement of switch arm I38 with contact I39 places the resistance 221 in parallel with relay winding I42 so that the current flow through both the relay winding I42 and the resistance 221 traverses the relay winding I43. This circuit is as follows: secondary I12, wire I13, wire 223, wire 225 and relay winding I43, at which point the circuit branches, part going by way of relay winding I42, wire 223, wire 224 and wire I14 to the other side of secondary I12 whereas the other portion goes by way of wire 229, resistance 221, wire 238, switch arm I38, contact I39, wire 233 and wire 224 to wire I14 and the' same side of secondary I12. Plunger I44 therefore moves to the right and switch arm I45 is moved into engagement with'contact I 41.

Engagement of switch arm- I38 with contact I39 also sets up an auxiliary circuit through solenoid coil I35 and resistance 223 which is as follows: secondary I12, wire I13, wire 2I8, solenoid coil I35, wire 22I, wire 232, resistance 228, wire 23I, wire 238, switch arm I38, contact I39, wire 233, wire 224 and wire I 14 to the other side of secondary I12. This auxiliary circuit for solenoid coil I35 increases the pull on armature or plunger I31 so as to maintain switch arm I 38 in firm engagement with contact I39. Field winding I58 is energized, upon engagement of switch arm I45 and contact I 41, through a limit switch 245, by a circuit which is as follows: line wire 243, switch arm I45, contact I41, wire 241, limit switch 245, wire 248 and field winding I58 to line wire 249. Rotor I52 is therefore rotated in a counter-clockwise direction as viewed from the left and main operating shaft I54 is operated in the same direction. Valve I53 is therefore moved towards closed position and balancing contact I3I moves downwardly along balancing resistance I38. When balancing contact I3I reaches the extreme lower end of balancing resistance I38, the solenoid coil I35 is substantially completely short-c'ircuited, complete short-circuiting beingprevented by reason of the protective resistance 2I2. This partial short-circuit is as follows: from the junction of solenoid coils I35 and I33, wire 22I, wire 222, balancing contact I3I, wire 2I5, protective resistance 2I2 and wire 2 to the left hand end of solenoid coil I35. Theenergizations of solenoid coils I33 and I33 are therefore substantially equal and plunger I31 moves far enough to the right to disengage switch arm I38 from contact I39. The resistance 221 is therefore removed from its parallel relationship with relay winding I42 and relay wind,-

is directly connected to wire I13, then the opposite action takes place. Under these conditions, solenoid coil I84 is'substantially completely short-circuited, complete short-circuiting again being prevented by inclusion of resistance I83. This partial I short-circuit is as follows: from the Junction of solenoid coils I 84 and I83, wire I81, resistance I83, wire I88, wire I83, bimetallic element .I83,'.contro1 contact I82, wire I13, wire I13 and wire I11 to the left-hand end of solenoid coil I84. Solenoid coil I83 is now more highly energized than solenoid coil I84 and plunger I83 moves to the right and brings switch arm I 81 into engagement with contact I89. The resistance I93 is now placed in parallel with relay winding II2 and the circuits for relay windings III and H2 and resistance I93 are as follows: secondary I12, wire I14, wire I92, wire "I and relay winding I II, at which point the circuit splits, part going by way of relay winding II2, wire I93, wire I94 and wire I13 to the other side of secondary I12, whereas the other portion goes by way of wire I91, resistance I93, wire I99, switch arm I81, contact I89, wire 282, and wire I94 to wire I13 and the same side of secondary I12. Relay winding III is therefore more highly energized than relay winding H2 and switch arm H4 is moved into engagement with contact III. Engagement of switch arm I 81 and contact I89 also sets up an auxiliary circuit through solenoid coil I83 and resistance I93 which is as follows:

secondary I12, wire I14, wire I18, solenoid coil I83, wire I89, wire 288, resistance I93, wire I99. wire I98, switch arm I81, contact I89, wire 282, wire I94 and wire I13 to the secondary I12. Field winding H8 is energized by engagement of switch arm H4 and contact II3, through a limit switch 258, by the following circuit: line wire 2, switch arm II4, contact II3, wire 25I, limit switch 238, wire 232, and field winding II8 to line wire 244. Rotor I28 is therefore rotated in a clockwise direction as viewed from the left and main operating shaft I23 rotates in the same direction. This causes upward movement of rack I23 and consequent opening movement of valve I23. Such movement of main operating shaft I23 also causes movement of balancing contact I38 upwardly along balancing resistance I29.

When the balancing contact I38 has completely traversed balancing resistance I29, then solenoid coil I83 is substantially completely shortcircuited by a circuit as follows: from the Junction of solenoid coils I84 and I83, wire I89, wire I98, balancing contact I38, wire I94, protective resistance I88 and wire I83, to the right hand end of solenoid coil I83. Solenoid coils I84 and I83 are thereupon again substantially equally energized and plunger I83 moves to' the left so as to move switch arm I81 from engagement with contact I 89. Resistance I95 is thereupon removed from its parallel relationshipwith relay winding H2, and switch arm II4 disengages contact I I3 thereby deenergizing field winding III. This separation of switch arm I81 from contact I89 also interrupts the auxiliary circuit through solenoid coil I83 and resistance I93. Valve I23 is now completely opened.

Such engagement of control contact I82 with the extreme left-hand end of control resistance I8I operates upon the second follow-up mechanism in the manner Just described for the first follow-up mechanism. In other words, solenoid coil I33 is substantially short-circuited by the following circuit: from the junction of solenoid coils I33 and I33, wire 2I9, resistance 2I8, wire 226, wire I66, bimetallic element I62, control contact I02, wire I16, wire I12, and wire 2" to the left hand end of solenoid coil I26. Plunler I21 thereupon moves to the right and switch arm I26 engages contact I40. Resistance 221 is thereupon placed in parallel with relay winding I42 and the circuit for relay windings I42 and I42 and nsistance 221 is as follows: secondary I12, wire I14, wire 224, wire 222 and relay winding I42, at which point the circuit splits, one portion going by way of relay winding I42, wire 226, wire 226 and wire I12 to the opposite side of secondary I12 whereas the other portion goes by way of wire 226, resistance 221, wire 220, switch arm I26, contact I40, wire 234 and wire 226 to wire I12 and the same side of secondary I12. Relay winding I42 is therefore more highly energized than relaywinding I43 and plunger I44 moves to the left bringing switch arm I46 into engagement with contact I46. Engagement of switch arm I26 with contact I40 also sets up an auxiliary circuit through solenoid coil I26 and resistance 226 which is as follows: secondary I12, wire I14, wire 2I I, solenoid coil I26, wire 22I, wire 222, resistance 226, wire 23I, wire 220, switch arm I26, contact I40, wire 224, wire 226 and wire I12 to the opposite side of secondary I12. This auxiliary current fiow through solenoid coil I26 causes switch arm I26 to be held firmly in engagement with contact I40.

Engagement of switch arm I46 with contact I46 causes energization of field winding I46 through a limit switch 252 by a circuit which is as follows: line wire 246, switch arm I46, contact I46, wire 264, limit switch 262, wire 266 and field winding I49 to line wire 246. Rotor III is therefore rotated in a clockwise direction as viewed from the left and main operating shaft I64 is rotated in a similar direction. Rack I66 moves upwardly and valve I56 is moved towards open position. Such movement of main operating shaft I64 also moves balancing contact I6I upwardly along balancing resistance I60.

when balancing contact I6I has completely traversed balancing resistance I60,solenoid coil I26 is substantially short-circuited as follows: from the junction of solenoid coils I26 and I26, wire 22I, wire 222, balancing contact I6I, wire 2", protective resistance 2I2 and wire 2" to the right-hand end of solenoid coil I26. Solenoid coils I26 and I26 are thereupon substantially equally energized and plunger I21 moves towards the left sufilciently to disengage switch arm I36 from contact I40. The resistance 221 is therefore removed from its parallel relationship with relay winding I42 whereupon relay windings I42 and I42 are again connected in series across the secondary I12 and are equally energized. Plunger I44 therefore returns to its central position wherein switch arm I46 is disengaged from contact I45. Field winding I46 is thereupon deenergized. Disengagement of switch arm I26 from contact I40 also interrupts the auxiliary fiow of current through solenoid coil I26 and resistance 226 whereupon solenoid coils I26 and I26 are again equally energized. Valve I66 is now in its full open position.

In the foregoing description, two extreme posi tions of control contact I02 have been described so that the description of Fig. 3 is in conformity with the illustrations already set out in connection with Fig. 1 and Fig. 2. In actual practice, if the control contact I02 is controlled automatically by a condition responsive member such as the bimetallic element I02, the movements of control contact I62 along control resistance III will be relatively slow. As soon as this movement of control contact I62 in respect to control resistance III has been sui'ficiently great to unbalance the voltage drops across solenoid coils I04 and I66 suihciently to lightly engage switch arm I61 with either of contacts I06 or I06, a follow-up action will take place. The reason for the auxiliary current fiows described in connection with solenoid coils I04 and I05 is to immediately increase the contact pressure between the switch arm I01 and either of the contacts I06 or I66 upon the very light engagement between these parts. This insures a good firm contact. Plunger I I2 is thereupon operated as previously described to energize one or the other of field windings H6 or II9 to drive balancing resistance I in the proper direction to rebalance the voltage drops across solenoid coils I04 and I05 suiiiciently to barely separate switch arm I01 from the particular contact I06 or I09 with which it is in engagement. Immediately this separation takes place, as brought out in the above description, the auxiliary current flow through solenoid coil I04 or coil I05 is interrupted whereupon the separation between switch arm I01 and either of the contacts I66 or I66 is substantially increased so that further movement of the main operating shaft I22 cannot take place until there is a reasonable movement of control contact I02 in respect to control resistance IOI. As indicated above, the limit switches 240 and 250 are operated in the usual well-known manner to limit the extreme movements of main operating shaft I22. While for the sake of clearness the extreme positions have been shown as being reached by a balancing out process wherein the balancing contact I20 moves to the extreme end of balancing resistance I26, in actual practice the balancing out of the voltage drops across solenoid coils I04 and I05 is not relied upon for the extreme positions but the limit switches 240 and 250 are utilized to obtain exact stopping of the main operating shaft I22 when the desired extreme position is reached.

The above comments are all equally applicable to the second follow-up system which includes the solenoid coils I25 and I26 and the associated control apparatus.

For a more complete understanding of the manner in which these follow-up systems operate generally, reference may be had to the copending application of Lewis L. Cunningham, S. N. 673,236, which was filed May 27, 1933.

In this system of Fig. 3, the two follow-up systems will stay in exact step in relation to the position of control contact I02 for the same reason as set forth in connection with Fig. 2. In other words, the junctions of the two sets of solenoid coils I04 and I05 and I25 and I36 are individually connected to the control contact I02 through individual resistances I66 and 2 I6 so that even though control contact I02 goes to an extreme position and one of the balancing contacts I26 or I6I goes to an opposite extreme position, still only that set of solenoid coils which is directly associated with the particular balancing contact is rebalanced and the other set of solenoid coils is not balanced untilits own associated balancing contact resumes the proper position. It will therefore be evident that our invention provides a novel manner of connecting a plurality of follow-up systems in parallel with a single variable eontroiler and in such a manner that each particular follow-up system must assume the position demanded by the position of the controller. In addition, the system of the present invention includes the highly desirable commercial feature of increasing the contact pressure of that switching mechanism which is operated in a marginal manner rather than an on and off manner. As far as the switching mechanisms II|II-II6 and l45'I46-I4'I are concerned, these are in the nature of on and of! apparatus rather than marginal controls so that increasing the contact pressure therebetween is unnecessary. In the event that motor field windings I I8 and H9 and I49 and I50 are low voltage windings, then the intermediate relay may be eliminated and the relay windings may become the motor field windings. It should also be noted that the individual follow-up systems utilized in this invention are entirely capable of being controlled by individual controllers so that the follow-up mechanisms of the present invention may be utilized either individually or in a multiple system.

As an example of the values of the various resistances and impedances used in an operable set-up of the system of Fig. 3, the secondary I12 produces 20 volts, the control resistance I I'll is 100 ohms, the balancing resistances I29 and IE0 are each 135 ohms, the protective resistances I19, I80, 2I2 and 2I3 are 35 ohmseach, the resistances I86 and 2I8 are 50 ohms each, the resistances I96 and 228 are each 2400 ohms, the resistances I95 and 221 are each 35 ohms and the impedance of each set of series connected solenoid and relay coils I04 and I05, III and H2, I35 and I36, and I42 and I43 is 120 ohms.

It will be evident that a number of changes may be made in the details of the present invention, and particularly the values given above, without departing from the scope of the invention and we are therefore to be limited only in accordance with the appended claims.

We claim:

1. In a temperature control system, in combination, a single variable impedance controller, a pair of electrical follow-up systems concurrently controlled thereby, a temperature controlling device controlled by each of said followup systems, and a single source of electrical power connected to said controller and each of said follow-up systems, each follow-up system comprising a pair of normally electrically balanced electromagnetic coils, balancing impedance means therefor, motor means in control of the balancing impedance means, and impedance means associated with the electromagnetic means and balancing impedance means in a manner to cause each motor means to position its temperature controlling device in accordance with the position of said controller, at least one of the coils of each of said systems being connected together and to said controller.

2. In a multiple electrical follow-up system, the combination with a plurality of electrical follow-up mechanisms each comprising a normally electrically balanced relay means, motor means controlled by the relay means, and balancing impedance means controlled by themotor means operative to maintain the relay means electrically balanced, of a single variable impedance controller for unbalancing the energizations of the relays, means electrically connecting the relays of both of said mechanismstogether and to said controller, and impedance means associated with both said relay means and both said balancing impedance means to cause each motor means to move to a position corresponding to the condition of said controller in order to eilfect a rebalancing of the energlzation of its particular relay means.

3. The combination with a plurality of electrically balanced proportioning control systems each of which comprises relay means normally energized in a certain manner, motor mea' s operated thereby upon a disturbance of such energization and balancing impedance means operated by the motor means to restore such energization, of a single impedance controller, means electrically connecting said relays in parallel to said controller so as to cause the latter to be operable to vary the energization to each of said relay means, and impedance means connected to each of said relay means and its associated balancing impedance means in a manner to prevent restoration of such energization of the relay means. until the associated motor means reaches a position corresponding to the condition of said controller whereby all of said control systems are maintained in proper step.

4. In a multiple electrical follow-up system; in combination; a plurality of electrical followup systems each comprising a pair of normally equally energized electromagnetic coils, switching means controlled thereby, motor means controlled by the switching means and a balancing potentiometer controlled by the motor means and operative to maintain the energizations of said coils equal; a single control potentiometer connected to each of said pairs of coils and operative to unequalize the energizations thereof, and resistance means associated with each of said pairs of coils and its associated balancing potentiometer operative to permit equalization of the energizations of each pair of coils only when such associated balancing potentiometer has been operated to the position it would have to assume if only one follow-up system were being con trolled by said control potentiometer whereby a plurality of such follow-up systems may be operated from a single controller and maintained in proper step.

5. In a multiple electrical follow-up system; in combination; a plurality of electrical follow- -up mechanisms each comprising a pair of series connected electromagnetic coils, switching means controlled thereby, motor means, controlled by the switching means and a balancing potentiometer controlled by the motormeans and including a balancing resistance and a. balancing contact; a single source of power; a single control potentiometer including a control resistance connected across said source of power and a control contact; a plurality of resistances; connections connecting said control contact to the junction of each pair of coils through a separate one N of said resistances; connections connecting the junction of each pair of coils to its associated balancing contact; connections connecting each pair of series connected coils across said source of power; and connections connecting each balancing resistance in parallel with its associated series connected coils.

potentiometer including a control resistance connected across said source of power and a control contact; a plurality oi resistances; connections connecting said control contact to the Junction of each pair of coils through a separate one of said resistances; connections connecting the Junction 01' each pair of coils to its associated plete short circuiting of either coil by its balancing potentiometer.

7. In a multiple graduated control system; in combination; a source 01' power; a plurality of individual follow-up systems each comprising a pair of electromagnetic coils connected in series across said source of power, an open contact switch controlled thereby, motor means controlled by said switch, means including connections and impedance means controlled by said switch for changing the energizations of said coils upon closure of said switch in a manner to increase the pressure of closing of said switch and impedance means controlled by said motor means and operative to equalize the energizations of said coils to cause opening of said switch; a single control impedance connected to each pair of coils and operative to change the energizations of the same; and impedance means associated with each pair of coils and said control impedance operative to keep each follow-up system in proper step with said control impedance.

8. The combination with a plurality of electrically balanced proportioning control systems each of which comprises electrical relay means normally energized in a. certain manner, electrical motor means operated thereby upon a disturbance of such energization and balancing resistance means operated by the motor means to restore such energization, of variable control resistance means electrically connected to each of said relay means and operable to vary the energization of each of said relay means, and resistance means connected to each of said relay means and its associated balancing resistance means in a, manner to prevent restoration of such energization of the relay means until the associated motor means moves to a position corresponding to the condition of the variable control resistance means whereby all of said control systems are maintained in .proper step.

9. The combination with a plurality of electrlcally balanced proportioning control systems each of which comprises plural coil electromagnetic means, an armature controlled thereby, switching means controlled by the armature, motor means controlled by the switching means, and balancing resistance means connected to at least one of the coils of said electromagnetic means and operated by the motor means in a manner to cause deenergization of the motor means whenever the motor means is energized, of means including control resistance means, and connections between said last-named means and at least one oi! the coils of each of said electromagnetic means electrically connecting said coils together and to said control resistance means and operable to vary the relative energizations of said electromagnetic means upon variation of said control resistance means to cause operation of aid switching means and to prevent deenergization of any of said motor means unless the motor means assumes a position corresponding to the condition of said control resistance means whereby all of said control systems are maintained in proper step.

10. In a temperature control system, in combination, a single variable impedance controller, a pair of electrical follow-up systems connected to and concurrently controlled thereby, a temperature controlling device controlled by each oi said follow-up systems and positioned thereby, a single alternating current source of electrical power for said controller and follow-up systems, and impedance means in the connections between said controller and said follow-up systems effective to cause each of said devices to move to the position corresponding to the position of the controller.

11. In a multiple electrical follow-up system, in combination, a plurality oi electrical follow-up systems each comprising electrical relay means normally energized in a certain manner, electrical motor means operated thereby upon a disturbance of such energization and balancing impedance means operated by the motor means to restore such energization, variable impedance control means, means connecting the relay means of each of said systems together and to said control means to render said variable impedance control means operable to vary the energization of each of said relay means, and impedance means operative to permit restoration of the original energization of each relay means only when the associated balancing impedance means has been moved to the position it would have to assume if only one follow-up system were being controlled by said control potentiometer whereby a plurality of such follow-up systems may be operated from a single controller and maintained in proper step.

12. In a multiple electrical follow-up system, in combination, a plurality of electrical follow-up systems each comprising electrical relay means normally energized in a certain manner, electrical motor means operated thereby upon a disturbance of such energization and balancing impedance means operated by the motor means to restore such energization, variable impedance control means, means connecting the relay means of each of said systems together; and to said control means to render said variable impedance. control means operable to vary the energization of each of said relay means and impedance means between said control means and each of said relay means operative to permit restoration of the original energization of each relay means only when the associated balancing impedance means has been moved to'the position it would have to assume if only one follow-up system were being controlled by said control potentiometer whereby a plurality of such follow-up systems may be operated from a single controller and maintained in proper step.

13. In a multiple electrical follow-up system, in combination, a. plurality of electrical follow-up mechanisms each comprising a pair of series connected electromagnetic coils, motor means controlled in accordance with the energization of said coils, and a balancing potentiometer controlled by the motor means and including a balancing resistance and a balancing contact, a single source of power, a single control potentiometer including a control resistance connected across said source of power and a control contact, a plurality of resistances, connections connecting said control contact to the junction of each pair of coils through a. separate one of said resistances, connections connecting the junction of each pair oi coils to its associated balancing contact. connections connecting each pair of series connected coils across said source of power and connections connecting each balancing resistance in parallel with its associated series connected coils.-

14. In a. motor control system, in combination, a single variable impedance controller, a plurality of electrical follow-up systems connected to and concurrently controlled thereby, each of said lollow-up systems comprising a motor and a device variably positioned thereby, a single alternating current source of electrical power for said controller and follow-up systems, and impedance means in the connections between said controller and said follow-up systems effective to cause each of said devices to move to the position corresponding to the position of the controller. 

